An electric motor may feature a rotor with permanent magnets and a stator, such as an interior permanent magnet (IPM) motor, an IPM synchronous motor, a surface mount permanent magnet motor, or another permanent magnet motor configuration. An electric motor may be used for vehicle propulsion, which often requires a wide speed range of motor control.
A stall condition means that a torque load is applied to an electric motor that causes the shaft speed of the motor to become or approach zero revolutions per minute. For example, a stall condition may be experienced if a vehicle propelled by an electric motor starts from a stationary position, if the vehicle is heavily loaded, if a vehicle is pulling a trailer or implement, or if the vehicle is heading up incline. At lower operational speeds that approach a stall condition, the electric motor may experience transient torque ripple, torque output oscillation or variable torque output. The passenger or operator of a vehicle may notice or complain about oscillatory, jittery or jerky movement of a vehicle with transient or variable torque output. Thus, there is a need for a method and system for controlling an electric motor at or near stall conditions to provide a uniform or stable torque output at lower operational speeds that approach a stall condition.